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Beau Zabel came to Philadelphia from a small town in Minnesota. He was studying to be a math teacher when he was shot to death, police say, for his iPod on June 15, 2008.

Updated at 7:19 PM EDT on Thursday, Nov 14, 2013

Five years after 23-year-old grad student Beau Zabel was shot to death leaving a Starbucks in South Philadelphia, police are prepared to issue an arrest warrant for the man they say pulled the trigger.

That man, Marcellus Jones, 35, is already serving time for another murder.

Zabel, who was from Minnesota, was a grad student at Drexel University. In the summer of 2008, he was also working at the Starbucks on 4th and South Street. As he was walking from work to his home in the Italian Market neighborhood, Zabel was shot to death.

"Well, it's been part of the investigation. But it was brought out in court that the motive for the killing of Taylor was his knowledge of Jones' involvement in the killing of Zabel," Philadelphia police Lieutenant Mark Deegan said last summer when he talked to NBC10's Deanna Durante about the Zabel investigation.

At that point in time, Deegan said even though other people told investigators that Jones killed Zabel, they needed more evidence to link Jones to Zabel's murder. Last summer, after Jones' conviction, Zabel's father said, "We do believe Marcellus Jones is the one who killed Beau. But without more proof he's almost never going to be convicted for that," Terry Zabel said.

An arrest warrant will be issued soon, according to law enforcement sources close to the investigation who did not want to be named because they were not authorized to speak publicly about the case.